The invention relates to a method for controlling a process with a set point which is variable and which can be changed to encompass the entire domain of the system. The invention particularly relates to a method for controlling the ignition timing of a spark plug ignited internal combustion engine in dependence on a plurality of variable operational parameters which affect the set point value, for example the engine speed (rpm), induction tube pressure, temperature, engine load, etc.
Known in the art are methods for controlling systems in dependence on operational parameters by changing the set point value. In many of these known methods, for example in methods for controlling a process, the set point value which governs the controlled variable changes according to predetermined functions which often are influenced additionally by the actual parameters of the sometimes very complicated control system. This means that a multitude of data must be collected in order to form the set point value which is later to be compared with the prevailing actual value and these data must be translated and processed with the aid of complicated circuitry such as transducers and/or function generators. The set point value which is a variable that depends on a multitude of such information is determined at each point of time and in every operational domain of the engine and is transmitted for example as a voltage to a summation point or a comparator in the control system.
Even when the systems to be controlled are relatively simple, the amount of effort and hardware required to produce the set point value is quite substantial and is not always justified by the results, for the basic purpose of any control system is to prevent any increasing excursion of the position of the final control element and this is achieved by feeding back a signal proportional to the actual value to the input of the system so that the entire process or system is controlled rigidly.
The present invention recognizes and makes use of the fact that, in a large number of processes in many technical areas, the error accumulation never exceeds a limiting value even if no feedback control is employed for considerable periods of time.